JOHANNESBURG (Reuters) - Nigeria's Nobel Prize-winning author Wole Soyinka has torn up his United States green card and renounced his American residency in protest at Donald Trump's U.S. election win, the writer told news channel eNCA on Thursday.

"I've done it," said Soyinka, 82, when asked if he had followed through on an earlier vow to leave the United States if Trump triumphed in the race for the White House.

"When I was ready, when I'd finished, I negotiated my departure," the Nigerian born author said in Johannesburg on the sidelines of a university conference.

Soyinka has had regular teaching stints at America's ivy league universities since the mid 1990s following his Nobel Prize for Literature in 1986. He was the first African writer to win the award.

A frequent and fierce critic of his own government, particularly over the carnage being inflicted by Boko Haram militants in northeastern Nigeria, Soyinka said he felt ill at ease in the wake of Trump's shock victory.

"We on the African continent could boast that we had a contemporary descendent ruling the United States," Soyinka said referring to outgoing President Barack Obama, whose father was a Kenyan.

"Suddenly, somebody is making speeches which are meant to reverse those gains."